Treatment of hydrocarbon distillates



Nov. 4, 1952 J. A. CH ENICEK ET AL TREATMENT OF HYDROCARBON DISTILLATESFiledMa'rch l, 1951 lull mummDmum orrwqzu INVENTORSZ mm NM. m M CM. R 0A T T T, W A m WE U f Patented Nov. 4, 1952 TREATMENT OF HYDROCARBONDISTILLATES Joseph A. Chenicek, Bensenville, and Kenneth M. Brown,Hinsdale, Ill., assignors to Universal Oil Chicago, 111., a corporationProducts Company, of Delaware Application March 1, 1951, Serial No.213,348

9 Claims.

This invention relates to the treatment of a sour hydrocarbon distillateand more particularly to a novel combination process to produce asubstantially sweet hydrocarbon distillate, which is substantially freefrom gum forming components, by a series of mutually related andinterdependent steps.

One method of treating hydrocarbon distillates containing mercaptansisto subject the distillate to treatment with caustic solutions in orderto remove a substantial proportion of the mercaptans therefrom. Whentreating a cracked gasoline, the final sweetening maybe effected byadding a phenylene diamine compound to the gasoline and allowing thegasoline to remain in storage until it becomes sweet. Because thephenylene diamine compound also serves as an oxidation inhibitor, thismethod of treating is referred to as inhibitor sweetening. However, ithas been found that, with some gasolines, this method of treatingresults in the desired sweetening but also results in an excessiveincrease in the gum content of the gasoline. The present invention isdirected to a novel method of retaining the benefits of the inhibitorsweetening and at the same time reducing gum formation.

In one embodiment the present invention relates to a combination processfor producing a substantially sweet hydrocarbon distillate of reducedgum formation which comprises treating a sour hydrocarbon distillatewith an alkali metal hydroxide to remove a substantial proportion of themercaptans contained therein, regenerating the used alkali metalhydroxide, commingling a phenylene diamine compound with thetreatedhydrocarbon distillate and allowing the resultant mixture to remain instorage in the presence of air until the distillate is substantiallysweet, and scrubbing the substantially sweetdistillate with theregenerated alkali metal hydroxide.

In a specific embodiment the present invention relates to a combinationprocess for producing a substantially sweet gasoline of reduced gumformation which comprises treating a sour cracked gasoline with acaustic solution previously used in the process in the manner to behereinafter set forth, regenerating the used caustic solution,commingling from about 0.001% to about 0.1% by weight ofN,N-di-secondary-bu tyl-p-phenylene diamine with the treated gasoline,subsequently treating the last mentioned gasoline with the regeneratedcaustic solution, and utilizing the caustic solution 'from the lastmentioned treating as said first mentioned caustic solution.

The novel combination process of the present invention is explainedfurther in the accompanying diagrammatic flow drawing which illustratesone specific embodiment thereof.

The novel combination process is particularly applicable to thetreatment of sour cracked gasolines, although it is understood that itmay be employed, with suitable modifications, for the treatmentof othercracked products including cracked kerosene, cracked light gas oil,etc'., as well as for the treatment of substantially saturatedhydrocarbon distillates including straight run gasoline, naturalgasoline, kerosene, gas oil,

etc V In the interest of simplicity the following description will bedirected to the treatment of a sour cracked gasoline also containinghydrogen sulfide. This is the normal gasoline production recovered froma cracking operation. Referring to the drawing, the gasoline isintroduced through line i to 'prewash zone 2. wherein it is contactedwith caustic introduced through line 3. Any suitable system may beemployed to remove the hydrogen sulfide from the cracked gasoline andthis may comprise either a batch or continuous type of operation. Thecaustic utilized in this step of the process generally is of low gravityof below about 20 Baum and/or has been used previously in otherprocesses. The used caustic from this step contains sodium sulfideswhich are difiicult to regenerate and, in most cases, it has been foundto be more economical to discard rather than to undergo the time andexpense of regenerating the same. The used caustic may be removed fromzone 2 through line 4 and may be discarded or further handled asdesired.

The gasoline now substantially free from hydrogen sulfide is withdrawnfrom zone 2 through line 5 and is directed to caustic scrubber 6. In theparticular case here illustrated, the gasoline in zone 6 is passed incountercurrent fiow with casutic solution previously used in the mannerto be hereinafter set forth in detail. The caustic solution isintroduced into zone 6 by way of line 1. Zone 6 may contain any suitablecontacting means including bubble trays, baflle plates, side to sidepans, etc. or it may be packed with suitable packing material, such ascarbon Raschig rings, etc.

" The caustic scrubbing in zone 6 may be effected at any suitabletemperature which generally will be about atmospheric. However, thetemperature may range from about'50 toabout 200 F. When desired, asolutizer also may be included in the caustic in order to improve theefliciency of the mercaptan extraction. Suitable solutizers includealcohols and particularly methyl alcohol, ethyl alcohol, propyl alcohol,etc. isobutyrates such as potassium isobutyrate, sodium isobutyrate,etc., alkali metal salts such as sodium phenolates, cresylates,xylenolates, similar potassium salts, etc. It is understood that inplace of caustic solution, other suitable alkali metal hydroxidesolutions may be employed, including potassium hydroxide, etc.

In zone 6 a major proportion of the mercaptans contained in the gasolinewill be removed through the formation of sodium mercaptides. The causticsolution containing sodium mercaptides is withdrawn from zone 6 throughline 8 and is subjected to regeneration in regenerator 9.

The caustic solution for use in accordance with the present inventionmust be of a gravity of at least Baum and preferably is of from about toabout 48 or more Baum gravity. This is an essential feature of thepresent invention because, for the reasons to be hereinafter set forth,it is necessary that a strong caustic solution be used in the subsequenttreating step of the process in order to remove the hydroperoxides whichare responsible for the formation of gum in gasoline.

The used caustic solution introduced into regenerator 9 is treatedtherein in any suitable manner in order to regenerate the causticsolution and to remove the mercaptans therefrom. In one method steam isintroduced through line It and the steam serves to hydrolyze themercaptides and to strip out the mercaptans, which are removed from zone9 through line II. In another method the regeneration may be effected byindirect heating, in which case a heating coil or other suitable meansis disposed in the lower portion of the regenerator and a suitableheating medium is .passed therethrough. In any event, a regeneratedcaustic solution of at least 30 Baum gravity is withdrawn from the lowerportion of regenerator 9 through line I2 for further use in the processin the manner to be hereinafter set forth in detail.

The treated gasoline from caustic scrubber 6 will now be substantiallyreduced in mercaptans and is withdrawn from zone 6 through line I3.Because the inhibitor sweeting reaction comprises the oxidation ofmercaptans to disulfides, it is necessary that air be present in thesweetening step of the process. Generally sufficient air will beentrained 0r dissolved in the gasoline to efiect the desired oxidationand it will be unnecessary to introduce air from. an extraneous source.However, when sufficient air is not contained in the gasoline, air froman extraneous source may be introduced through line I4 to commingle withthe gasoline in line I3.

In the case here illustrated, a phenylene diamine compound is introducedthrough line I5 and is commingled with the gasoline in line I3, and theresultant mixture is directed into inhibitor sweetening zone I6. Itgenerally is preferable to pass. the mixture. in. line I3 through asuitable mixing device, such as a duriron mixer, an orifice mixer, etc.,illustrated at IT, in order to obtain intimate mixing of the gasolineand phenylene diamine compound. It is understood that the, phenylenediamine compound and/or air may be introduced directly to inhibitorsweetening zone I6, in which case zone I6 preferably includes suitablemixing means, such as mixing paddles, illustrated at I8. Inanothermethod, the. desired mixing may be obtained by suitablecirculation of the mixture in zone I5. In still another method the airmay be introduced to zone I6 in such a manner that it will serve toefiect intimate mixing of the components therein.

Any suitable phenylene diamine compound may be employed in accordancewith the present invention and preferably comprises N,Ndi-secondarybutyl p phenylene diamine which is presently commercially marketed asUOP Inhibitor No. 5. Other phenylene diamine compounds includeN,N'-di-alkyl-p-phenylene diamines in which the alkyl groups containfrom one to about 12 carbon atoms per molecule, including such compoundsas N,N'-di-isopropyl-pphenylene diamine,N,N'-di-secondary-amyl-pphenylene diamine,N,N'-di-secondary-hexyl-pphenylene diamine,N-isopropyl-N-secondarybutyl-p-phenylene diamine,Nisopropyl-N-secondary-amyl-p-phenylene diamine, etc. The phenylenediamine compound is utilized in a concentration of less than about 1% byweight and preferably of from about 0.000.l% to about 0.1%.

Inhibitor sweetening in zone I6 generally will be effected within acomparatively short time which, preferably should not be more than about24 hours. The. inhibitor sweetening generally is effected atsubstantially atmospheric temperatures which usually range from about 50to about F. However, when desired, the inhibitor sweetening may beefiected at a higher temperature which may range up to F. or more; andthis may be accomplished by introducing the gasoline through line I3 atthe desired temperature and/or by heating zone I 6 in any suitablemanner, such as by the use of suitable heatin coils disposed therein inorder to heat and/or maintain the components therein at the desiredtemperature.

After the desired time in storage the gasoline, which now issubstantially sweet, is withdrawn from zone I6 through line I9 and isintroduced to caustic scrubbing zone 20. Zone 20 may contain suitablecontacting means as hereinbefore described in connection with zone 6,and the caustic scrubbing therein may be effected at substantially thesame temperature as heretofore described for zone 6. In the case hereillustrated, the substantially sweet gasoline is passed incountercurrent contact in zone 20 with the regenerated caustic solutionintroduced thereto through line I2. As hereinbefore set forth, it is anessential feature of the present invention that the caustic solutionused in zone 20 be of at least 30 Baum gravity and preferably in fromabout 40 to 48 or more Baum gravity.

The reason why it is essential to use a strong caustic solution in zone20 is believed to be as follows, although it is understood that we arenot limited to this specific explanation. Cracked gasolines containdimcultly removable mercaptans, such as tertiary alkyl mercaptans. Thesemercaptans are not removed by caustic scrubbing in zone 6 and willremain in the gasoline supplied to inhibitor sweetening zone I6. Duringthe inhibitor sweetening reaction, the tertiary alkyl mercaptans, forexample, react to form free radicals which in turn react with olefinsand oxygen to form hydroperoxide free radicals. The hydroperoxide freeradicals can react with mercaptans with the formation of disulfides orthey can. be instrumental in catalyzing oxidation reactions. leading togum formation. Since the mercaptans which react most readily with thehydroperoxide free radical are those which are most easily removed fromthe gasoline by caustic scrubbing in zone 8, these mercaptans are notavailable for reaction with-the hydropenoxide free radical and,therefore, the reaction-results in the formation of hydroperoxides whichlead to gum formation in the gasoline if they are not-removed. Inaccordance with the present invention, the hydroperoxides are removedfrom the gasoline in caustic scrubbing zone l and this requires a strongcaustic solution as hereinbefore set forth.

The caustic solution containing the hydro peroxides is withdrawn fromzone 20 through line 2| and is directed by way of line I, to'be utilizedin caustic scrubber 6 to treat the gasoline containing mercaptans. Inzone 6 the-hydroperoxides react with the mercaptans to form disulfides.As hereinbefore set forth, the formation of disulfides will occur inzone 6 because the readily re-' actable mercaptans are present in this.zone but will not occur in zone 20 because these readily reactablemercaptans are not present in zone 20.

In another embodiment of the invention the caustic solution withdrawnfrom zone '20 may be directed through line 2| to caustic regenerator 9.In caustic regenerator 9 the hydroperoxide sodium salts are decomposedto sodium hydroxide and to oxygen-containing hydrocarbons presumablyalcohols, and the latter are stripped from the caustic in regenerator 9and arewithdrawn with the mercaptans through line I I.

The treated gasoline from zone 20 is withdrawn therefrom through line 22and, as hereinbefore set forth, the gasoline is substantially sweetandis reduced in gum forming components.

In the interest of simplicity, valves, pumps and similar appurtenanceshave been omitted from the drawing but it is understood that they willbe used as required. It is also understood that, when solutizers orother materials are to be utilized in the process, they may beintroduced in any suitable manner and also that the requiredfractionation or other separating means will be included.

The following examples are introduced to illustrate further the noveltyand utility of the present invention but not with the intention ofunduly limiting the same. 7

Example I A cracked gasoline containing hydrogen sulfide and mercaptansmay be treated with a caustic solution of Baum gravity in a batch typeoperation to remove hydrogen sulfide. The gasoline free from hydrogensulfide is then subjected to treatment with a caustic solution of 48Baumgravity to remove a substantial proportionof the mercaptans. The usedcaustic is regenerated by steam stripping. The caustic scrubbed gasolineis then commingled with 0.005% by weight of N,N' disecondary-butyl-p-phenylenefidiamine and,'after passing through aduriron mixer, is sent to a storage tank and allowed to; remain thereinfor 24 hours. The gasoline from the storage tank is then scrubbed withthe regenerated caustic solution of 48 Baum gravity, and the sed caustictherefrom employed for-{treating the gasoline in the caustic scrubbingtreatment. The caustic scrubbing and inhibitor sweetening operation areall efiected at substantially atmospheric temperature. The gasolinewithdrawn from the last caustic scrubbing will be .substantially sweetand of reduced gum contentl For example, the gasoline when) causticscrubbed and inhibitor sweetened without the I final caustic treatmentof the present combination process may have a copper dish gum content ofabove 150 mg. after 2 days in storage. 0n theother hand, when treated bythe combination process of the present invention, the gasoline may havea copper dish gum content of less than about Example II Cracked gasolinemay be treated in substan tially the same manner as described in ExampleI but using 0.02% by weight of N,N-di-isopropyl-,

p-phenylene diamine as the inhibitor and sweetening agent.

Example III Cracked light gas oil may be treated in substantially thesame manner as described in Example I but using 0.01 by weight ofN,N-di-secondary-butyl-p-phenylene diamine and effecting the inhibitorsweetening at a temperature of F; V n y Example IV A straight rungasoline containing mercaptans is treated in substantially the samemanner as described in Example I but in this case the in: hibitorsweetening reaction is effected at atem perature of F.-

We claim as our invention:

1. A combination process for producing a substantially sweet hydrocarbondistillate of reducedgum formation which comprises treating a sourhydrocarbon distillate with an alkali metal hydroxide to remove asubstantial proportion of the mercaptans contained therein, regeneratingthe used alkali metal hydroxide, commingling a phenylene diaminecompound with the treated hydrocarbon distillate, and subsequentlytreating the hydrocarbon distillate with the regenerated alkali metalhydroxide.

2. A combination process for producing a substantially sweet hydrocarbondistillate of reduced gum formation which comprises treating asourhydrocarbon distillate with an alkali metal hydroxide solutionpreviously used in the process in the manner to be hereinafter setforth, regencrating the used alkali metal hydroxide solution,commingling a phenylene diamine compound with the treated hydrocarbondistillate and allowing the resultant mixture to. remain in storage inthe presence of air until the distillate is substantially sweet,subsequently treating the substantially sweet-distillate with theregenerated alkali metal hydroxide solution, and utilizing the alkalimetal hydroxide solution from the last mentioned treating step as saidfirst mentioned alkali metal hy-. droxide solution. Y

3. A combination process for producing a sub stantially sweethydrocarbon distillate of reduced gum formation which comprises treatinga hydrocarbon distillate containing hydrogen sulfide and mercaptans withcaustic solution of below about 20 Baum gravity-to remove hydrogensulfide, separating a hydrocarbon distillate free of hydrogen sulfideand treating the same with caustic solution of at least 30 Baum gravityto remove a substantial proportion of the mercaptans from saiddistillate,lregenerating the used caustic solution to ,recoveii aregenerated caustic solution of at least 30 .Baum gravity, comminglingN,N'-di-secondary butyl-p-phenylene diamine in an amount of not morethan about 1% by weight with said treated hydrocarbon distillate andallowing the resultant mixture to remain in storage in the presenceotiair until the distillate is substantially sweet, subsequentlytreating the substantially sweet distillate with the regenerated causticsolution of at least 30 Baum gravity,

and utilizing the caustic solution from thelast mentioned treating assaid first mentioned caustic solution of at least 30 Baum gravity;

4. A combination process for producing a substantially sweet gasoline ofreduced gum formation which comprises treating a sour gasoline with analkali metal hydroxide solution previously used in the process in themanner to be hereinafter set forth, regenerating the used alkali metalhydroxide solution, commingling a phenylene diamine compound in anamount of not greater than about 1% by weight with said, gasoline,subsequently treating the last mentioned gasoline with the reregeneratedcaustic solution, and utilizing the caustic solution from the lastmentioned treat ing as said first mentioned caustic solution.

5. A combination process for producing a substantially sweet gasoline ofreducedgum formation which comprises treating a sour cracked gasolinewith a caustic solution previously employed in the process in themanner. to .be hereinafter set forth, separating. causticsolution from.

treated gasoline and regenerating the caustic solution, commingling fromabout 0.001% to about 0.1% by weight ofN,N--di-secondarybutyl-p-phenylene diamine with the treated gas oline,subsequently treating the last mentioned gasoline vwith the regeneratedcaustic solution, and employing the caustic solution fromthe lastmentioned treating as said first mentioned caustic solution. Y

6.. A combination process for producing a substantially sweet gasolineof reduced gum formation which comprises treating a cracked gasolinecontaining hydrogen sulfide and mercaptans with a caustic solution ofless than about Baum gravity to remove the hydrogen sulfide, separatingcracked gasoline substantially free of hydrogen sulfide and treating thesame with a caustic solution of at least 40 Baum gravity to remove asubstantial proportion of the mercaptans from the gasoline, separatinggasoline of reduced mercaptan content from the used caustic solution,regenerating the used caustic solution to form a caustic solution of atleast 40 Baum gravity, commingling from about. 0.00l to about 0.1% byweight of N,N'-di-secondarybutyl-p-phenylene diamine with the lastmentioned gasoline and allowing the resultant mixture to remain instorage in the presence of air until the gasoline is substantiallysweetbut contains hydroperoxides, subsequently scrubbing the substantiallysweet gasolinewith the regenerated caustic solution of at least 40 Baumgravity to remove hydroperoxides fromth'e gasoline, and

react with the mercaptans contained. in the j l gasoline to. formdisulfides, v a

- 7. A combination process for producing a' sub-- stantially sweetgasoline of reduced gum formation which comprises treating a sourgasoline with a caustic solution of at least 40 Baum gravity to remove asubstantial proportion of the mercaptans from the gasoline, separatinggasoline of reduced mercaptan content from the used caustic solution,regenerating the used caustic solution to form a caustic solution ofatleast 40 Baum gravity, commingling a phenylene diamine compound withthe last mentioned gasoline and allowing the resultant mixture to remainin storage in the presence of air until the gasoline is substantiallysweet but contains hydroperoxides, subsequently scrubbing thesubstantially sweet gasoline with the regenerated caustic solution of atleast 40 Baum gravity to remove hydroperoxides from the gasoline, andsupplying the resultant caustic solution containing hydroperoxides tothe first-mentioned treating step wherein the hydroperoxides are reactedwith mercaptans in said sour gasoline to form disulfides.

8. A process for producing a substantially sweet hydrocarbon distillateof reduced gum formation which comprises treating a sour hydrocarbondistillate with an alkali metal hydroxide solution of suflicientstrength to remove a substantial portion of the mercaptans containedtherein, regenerating the used alkali metal hydroxide solution, treatingthe distillate of reduced mercaptan content with a phenylene diaminecompound in the presence of air, thereby forming hydroperoxides in thedistillate, thereafter contacting the distillate with the regeneratedalkali metal hydroxide solution to remove hydroperoxid'es therefrom, andsupplying the resultant hydroperoxide-containing solution to thefirst-mentioned treating step wherein the hydroperoxides are reactedwith mercaptans in said sour distillate to form disulfides.

9.'The process of claim 8 further characterized in that said alkalimetal hydroxide solution is a caustic solution of at least 30 Baumgravity.

JOSEPH A. CHENICEK. KENNETH M. BROWN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,840,269 Borgstrom Jan. 5, 19322,183,968 McCormick et al. Dec. 19, 1939 2,427,212 Henderson et al.Sept. 9, 194'! 1 2,508,817 Devol et al May 23, 1950 2,543,953 BackenstcMar. 6, 1951 2,552,399 Browder- May 3, 1951

1. A COMBINATION PROCESS FOR PRODUCING A SUBSTANTIALLY SWEET HYDROCARBONDISTILLATE OF REDUCED GUM FORMATION WHICH COMPRISES TREATING A SOURHYDROCARBON DISTILLATE WITH AN ALKALI METAL HYDROXIDE TO REMOVE ASUBSTANTIAL PROPORTION OF THE MERCAPTANS CONTAINED THEREIN, REGENERATINGTHE USED ALKALI METAL HYDROXIDE, COMMINGLING A PHENYLENE DIAMINECOMPOUND WITH THE TREATED HYDROCARBON DISTILLATE, AND SUBSEQUENTLYTREATING